Field of the Invention
The invention relates to a catalytic converter for accelerating at least one reaction between at least two reactants of a gas mixture, including a catalyst carrier and a catalytically active substance.
In a number of technical and industrial applications, catalytic converters that are especially adapted to the particular reaction of the reactants and to the reaction conditions are used for the catalytic conversion of reactants of a gas mixture. Examples thereof are so-called oxidation catalytic converters and deNO.sub.x catalytic converters.
Oxidation catalytic converters, having catalytic activity which is determined essentially by the content of noble metals and/or oxides of the transition metals, catalytically convert carbon monoxide and hydrocarbons, for instance, into carbon dioxide and water, in the simultaneous presence of oxygen from the air. With that type of exothermic reaction, heating of the catalyst occurs, which favors undesirable side reactions, such as the formation of nitrogen oxides. DeNO.sub.x catalytic converters, in the simultaneous presence of ammonia, catalytically convert nitrogen oxides into nitrogen and water by the process of selective catalytic reduction (SCR). Flue gases in which nitrogen oxides are present usually also contain sulfur dioxide. Therefore deNO.sub.x catalytic converters, because of the catalytically active substances contained in them, favor the undesired side reaction of the conversion of sulfur dioxide SO.sub.2 to sulfur trioxide SO.sub.3. The ammonium sulfates that form at the catalytic converter from ammonia and sulfur trioxide are highly hydrophilic. If the temperature drops below the dew point, the ammonium sulfates adhere and stop up all of the components downstream, which is extremely disadvantageous.
Typical deNO.sub.x catalytic converters are manufactured on the basis of titanium dioxide TiO.sub.2, with one or more of the additives tungsten trioxide WO.sub.3, molybdenum trioxide MoO.sub.3 and vanadium pentoxide V.sub.2 O.sub.5. The catalytic activity is essentially determined by the content of vanadium pentoxide V.sub.2 O.sub.5 and V.sub.x Mo.sub.x O.sub.32-z. The aforementioned side reaction is made even stronger because, as a result of the preceding catalytic conversion, the content of ammonia and nitrogen oxides decreases in the flow direction of the flue gas in the catalytic converter. Due to the decrease of ammonia and nitrogen oxides, the catalytically active centers are increasingly used for SO.sub.2 /SO.sub.3 conversion.